Low back pain is a common disease which may be caused by herniated discs, compressed nerve roots, degenerative discs or joint disease.
If a patient suffers severe low back pain and does not respond to conservative treatment, spinal fusion is an option to eliminate the pain. Spinal fusion is a surgical technique wherein two or more vertebrae are joined together. Spinal fusion interventions are also performed to correct back deformities.
With spinal fusion, often an intervertebral spacer or device is placed between the involved vertebrae after removal of the intervertebral disc. The intervertebral device corrects the spine alignment and restores the disc height. Common intervertebral devices are made from titanium alloys or PEEK (polyetheretherketone) polymer. Often these devices comprise pockets that can be filled with bone graft material or artificial graft substitute. The fusion itself takes place when the bone of the vertebral endplates grows into and through the intervertebral device. Finally both vertebrae are grown together. Often, a pedicle system provides additional posterior stabilisation. Intervertebral fusion devices can be implanted with various approaches, for example with an anterior, posterior or lateral approach.
Over the past years minimally invasive techniques have been introduced. One advantage of the minimal invasive techniques is a reduction of soft tissue trauma resulting in a faster recovery. Other complications are reduced as well. In minimally invasive techniques the implant is brought into position between the vertebral bodies through a small incision with small instruments. However, the intervertebral device must still have a sufficient large foot-print to withstand the forces between the vertebrae before complete fusion has taken place. If a device has a too small foot-print it will sink into or break through an endplate of a vertebra, and the initially restored height is lost.
Combining advantages of the minimally invasive surgery approaches with intervertebral devices with large footprint affording a good support would require a device which may be brought into place through a small incision and which in a second step may be expanded to a larger size.